DESIGN AND DEVELOPMENT OF AN ADJUSTABLE CONSTANT FORCE MECHANISM

“Constant force mechanisms (CFMs) are widely used in various applications, including force regulators, surgical graspers, grippers, micro injectors, vibration isolation and constant force actuators. CFMs, designed for a single constant force, necessitate active mechanical control for force adjustability. The objective of this paper is to develop a semi-active, structural controlled adjustable CFM (ACFM) with a large change in constant force. A path based structural optimization is conducted using graphs. A 2x2 grid is selected, and nodal locations are perturbed to obtain a large stroke CFM with high quality constant force as defined by the energy similarity index, i.e., ratio of the energy capacity of the CFM to an ideal CFM. The slenderness of the CFM was tuned in order to change the constant force of the mechanism using a parametric study. The parametric study showed a change in constant force, maximum stroke and the quality of constant force as the slenderness was changed. In the experiment using a 2-layer unidirectional fiberglass specimen, slenderness was tuned by modifying a fixed boundary condition location in a fixed-fixed setup. The constant force (CF) was doubled from its value while maintaining a high energy similarity index of 0.9. Compared to mechanisms in the literature, the selected proposed mechanism was found to be 4.1% more compact. In conclusion, semi active control using boundary condition location adjustment in CFM was implemented for the first time to develop an ACFM. The ACFM is ideal for diverse applications including impact attenuation, vibration isolation, and surgical graspers.”